A hub-spindle assembly for a rotatable wheel and an associated stationary axle generally comprises, a hub, a spindle and one or more wheel bearings. The hub is a structure at the center of the wheel that houses the wheel bearings and the spindle. The spindle extends from the end of the axle into the hub and the wheel bearings are positioned between the spindle and hub to provide a friction-reduced surface therebetween as the hub and wheel rotate about the stationary spindle and axle. The hub encloses a chamber, within which the wheel bearings and spindle are housed. The chamber contains a viscous lubricant that lubricates the bearings of the hub-spindle assembly during rotational operation of the wheel.
A cap is typically provided over the front of the hub to seal the chamber from the external environment preventing the intrusion of contaminants therein, such as grit or moisture. Such contaminants can damage or accelerate wear of the bearings within the hub-spindle assembly, thereby diminishing the life of the bearings and necessitating frequent replacement, or in some cases causing failure of the assembly during operation with potentially catastrophic results. The cap is typically removable, however, to facilitate access to the interior of the lubricant chamber for inspection, servicing or replacement of the lubricant or assembly components.
The above-described hub-spindle assembly is conventional to virtually all types of conveyances employing rotatable wheels and stationary axles, including motor vehicles and trailers. However, there are specific operational requirements for marine trailers used to transport boats, jet skis, and the like that dictate unique design features for the attendant hub-spindle assemblies. In particular, marine trailers must be capable of frequent and sustained immersion in water when launching or loading water craft. Accordingly, the hub-spindle assembly, and specifically the lubricant chamber of the hub, must be impervious to water intrusion, which as noted above, undesirably promotes damage and wear of the assembly components.
Certain hub-spindle assemblies known in the art are designed specifically to obviate the problem of water intrusion into the lubricant chamber of marine trailers. For example, U.S. Pat. No. 5,054,859 discloses a hub, wherein a grease lubricant contained within the lubricant chamber is pressurized against the walls of the lubricant chamber by means of a cap having a spring-biased, slidable piston positioned therein. The cap permits expansion or contraction of the grease lubricant within the lubricant chamber as the temperature of the grease lubricant changes during operation of the hub-spindle assembly, thereby eliminating voids within the lubricant chamber that facilitate water intrusion. The outward pressure of the grease lubricant relative to the lubricant chamber also opposes the inward water pressure providing a positive resistive force against water intrusion into the lubricant chamber.
Despite the widespread use of grease lubricant-containing hubs in marine trailers, liquid lubricants are generally known to be more effective lubricating agents than grease lubricants in hub-spindle assembly applications. Liquid lubricants exhibit improved heat transfer properties relative to grease, thereby more effectively transferring heat away from the hub-spindle assembly during operation. In addition, Commercial-grade liquid lubricants usually contain a lower level of particulates than commercial-grade grease lubricants. Consequently, a hub-spindle assembly lubricated with a liquid lubricant tends to exhibit a slower rate of wear than one lubricated with a grease lubricant under equivalent operating conditions. The proliferation of grease lubricant-containing hubs is, however, attributable to the fact that liquid lubricant-containing hubs are operationally more problematic than grease lubricant-containing hubs. For example, liquid lubricant-containing hubs are often more prone to lubricant leakage and water intrusion during operation than grease lubricant-containing hubs. Conventional liquid lubricants are typically petroleum-based oils that are rendered less effective as lubricants when contaminated with water because their hydrophobic character renders them relatively insoluble in water.
U.S. Pat. No. 5,303,800 discloses a liquid lubricant-containing hub that obviates the problem of water intrusion. A hydrophilic liquid selected from among the glycols is used as the lubricant because it is relatively viscous yet is relatively solvent in water. The solubility of the selected glycol enables it to remain fully effective as a lubricant, even when contaminated with a substantial volume of water. The liquid lubricant-containing hub disclosed therein is further provided with an expandable bellows formed from a stretchable elastomeric material that encloses a portion of the lubricant chamber and permits expansion of the liquid lubricant within the chamber during operation of the hub-spindle assembly.
Operation of the liquid lubricant-containing hub disclosed in U.S. Pat. No. 5,303,800 has inherent problems, however. In particular, the lubricant chamber is only filled to about 20% of capacity with the liquid lubricant so that the bellows is maintained in a neutral position when the hub-spindle assembly is at rest. The centrifugal force created by rotation of the wheel during operation of the hub-spindle assembly is relied upon to distribute the liquid lubricant to the upper portions of the bearings that are not in contact with the liquid lubricant when the assembly is at rest. Unfortunately, marine trailers often have only seasonal usage and remain in storage for extended periods of nonuse. During such periods of nonuse, the exposed upper portions of the bearings not contacted by the liquid lubricant are susceptible to rust which is extremely deleterious to the future operability of the hub-spindle assembly.
Additionally, the elastomeric bellows obscure visual access to the lubricant chamber, thereby hindering visual inspection of the liquid lubricant level in the lubricant chamber. Consequently, leakage of liquid lubricant from the hub may go undetected resulting in unacceptably low lubricant levels for operation of the hub-spindle assembly. Finally, it is noted that glycols are not conventional lubricants and as such may be costly or difficult to obtain, particularly in remote locales of operation.
Accordingly, it is an object of the present invention to provide a capped hub that overcomes the problems encountered with prior art hubs such as described above. More particularly, it is an object of the present invention to provide a capped hub that employs a conventional liquid hydrocarbon lubricant. It is another object of the present invention to provide a capped hub employing a liquid lubricant that fully contacts the wheel bearings retained in the hub when the hub is at rest and in rotational operation. It is yet another object of the present invention to provide such a capped hub that has specific utility to marine trailers.
It is a further object of the present invention to provide a cap for a hub that accommodates expansion of the liquid lubricant contained within the hub. It is still a further object of the present invention to provide a cap for a hub that is resistant to intrusion of water or other contaminants into the lubricant chamber of the hub. It is yet a further object of the present invention to provide a cap for a hub that enables visual inspection of the liquid lubricant within the lubricant chamber of the hub without removal of the cap. It is another object of the present invention to provide a cap for a hub that is readily removable to provide access to the interior of the hub for servicing thereof. It is still another object of the present invention to provide a cap for a hub that is sufficiently sturdy to withstand rigorous operation. These objects and others are accomplished in accordance with the invention described hereafter.